1. Field of the Invention
The present invention relates to an electrostatic discharge protection device, and in particular to a cross-domain electrostatic discharge protection device for integrated circuits.
2. Description of the Related Art
Generally, integrated circuits will include multiple power domains. A device may, for instance, include an input/output (I/O) circuit along with a core circuit, each of which may be associated with a different power domain (e.g., the I/O circuit may be associated with a high-voltage power domain, the core circuit may be associated with a low-voltage power domain, etc.). Thus, signals may travel from a high-voltage power domain to a low-voltage power domain. Typically, from an electrostatic discharge (ESD) protection design point of view, one of the most critical issues of cross-domain interface circuits is gate oxide breakdown of low-voltage metal-oxide-semiconductor field-effect transistors (MOSFETs). For cross-power-domain ESD protection, ESD protection devices are required to be set between any pin-to-pin combination of voltage supplies or power nodes.
FIG. 1 shows an ESD protection scheme for cross-power-domain ESD protection. FIG. 2 shows an example of simple ESD protection for cross-power-domain. For example, two power domains VDD1-VSS1 and VDD2-VSS2 are applied in an integrated circuit (for brevity, the main portion and peripheral of the integrated circuit are not shown in FIGS. 1 and 2). In FIG. 1, using six ESD cells 11˜16 can provide full ESD protection for any path of VDD1-VSS1, VDD1-VSS2, VDD1-VDD2, VDD2-VSS1, VDD2-VSS2 and VSS1-VSS2, but it consumes too large an area. As a trade-off for area and cost requirements, some of the ESD cells may be removed. Thus, in FIG. 2, a simple ESD protection scheme is provided. The simple scheme consumes a smaller area, but its ESD protection is degraded since some direct paths (such as VDD1-to-VSS2 and VDD2-to-VSS1) are not protected.
Accordingly, it is desirable to propose a cross-domain ESD protection cell (device) with a novel structure capable of providing sufficient ESD discharge paths and consuming less of an area.